Question 1

Which of the following best describes the First Law of Thermodynamics?

Accepted Answer

The total energy of the universe is constant; energy can be transferred or transformed but not created or destroyed.

Question 2

A 50.0 g piece of metal at 120.0 °C is placed in 100.0 g of water at 22.0 °C. The final temperature is 26.5 °C. If the specific heat capacity of water is $$4.18\ \mathrm{J\cdot g$$^{-1}$$\cdot ^\circ C$$^{-1}$$}$$, what is the heat gained by the water?

Accepted Answer

$$q = (100.0\ \mathrm{g})(4.18\ \mathrm{J\cdot g$$^{-1}$$\cdot ^\circ C$$^{-1}$$}})(4.5\ ^\circ C) = 1881\ \mathrm{J}$$

Question 3

Which of the following is a state function?

Accepted Answer

Internal energy ($$U)$$

Question 4

A gas expands from $$1.50\ \mathrm{L} to$$ $$4.25\ \mathrm{L}$$ against a constant external pressure of $$95.0\ \mathrm{kPa}. $$What is the work done by the gas? ($$1\ \mathrm{kPa\cdot L} = 1\ \mathrm{J})$$

Accepted Answer

$$w = -261\ \mathrm{J}$$

Question 5

Which process is exothermic?

Accepted Answer

Combustion of methane

Question 6

In a bomb calorimeter, a $$1.50\ \mathrm{g}$$ sample of fuel is burned, raising the temperature of the calorimeter (heat capacity $$9.80\ \mathrm{kJ\cdot ^\circ C$$^{-1}$$}) by$$ $$2.35\ ^\circ C. $$What is the heat released by the reaction?

Accepted Answer

$$q = (9.80\ \mathrm{kJ\cdot ^\circ C$$^{-1}$$})(2.35\ ^\circ C) = 23.0\ \mathrm{kJ}$$

Question 7

Which of the following statements about enthalpy ($$\Delta H) is $$correct?

Accepted Answer

$$\Delta H is $$the heat exchanged at constant pressure.

Question 8

Which of the following best describes the difference between temperature and thermal energy?

Accepted Answer

Temperature is a measure of the average kinetic energy; thermal energy is the total energy due to molecular motion.

Question 9

Which of the following is true about standard enthalpy of formation ($$\Delta_f H^\circ$$)?

Accepted Answer

It is the enthalpy change when 1 mole of a compound forms from its elements in their standard states.

Question 10

A reaction has $$\Delta H = -56.4\ \mathrm{kJ\cdot $$mol^{-1}$$}. $$Which statement is correct?

Accepted Answer

The reaction is exothermic and releases heat to the surroundings.

Question 11

Which equation correctly expresses the First Law of Thermodynamics for a system?

Accepted Answer

$$\Delta U_{sys} = q + w$$

Question 12

Which calorimeter is best suited for measuring the heat of combustion of a fuel?

Accepted Answer

Bomb calorimeter

Question 13

Which of the following is a real-world example of an endothermic process?

Accepted Answer

Using an instant cold pack

Question 14

If a reaction is carried out in a bomb calorimeter, which thermodynamic quantity is directly measured?

Accepted Answer

$$\Delta U$$

Question 15

Which of the following statements about Hess’s Law is correct?

Accepted Answer

The enthalpy change of a reaction is the sum of the enthalpy changes of the steps into which the reaction can be divided.

Question 16

A 55.0 g iron cube at 99.8 °C is placed in 225.0 g of water at 21.0 °C. The final temperature is 23.1 °C. What is the specific heat capacity ($$C_s) of $$the iron? ($$C_{water} = 4.18\ \mathrm{J\cdot g$$^{-1}$$\cdot ^\circ C$$^{-1}$$})$$

Accepted Answer

$$C_s = 0.469\ \mathrm{J\cdot g$$^{-1}$$\cdot ^\circ C$$^{-1}$$}$$

Question 17

Which of the following best describes the energy changes in the combustion of methane?

Accepted Answer

Chemical potential energy is converted to thermal energy, which is released to the surroundings.

Question 18

Which of the following is NOT a correct energy unit conversion?

Accepted Answer

1 J = 1 cal

Question 19

Which of the following statements about energy and the environment is correct?

Accepted Answer

Combustion of fossil fuels releases energy and contributes to environmental issues such as greenhouse gas emissions.

Chapter 6: Thermochemistry – Study Notes

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